PI: Waggoner, Stephen Noel, ?Targeting natural killer cells to enhance HIV vaccine responses? ABSTRACT Immunization represents one of the most successful public health interventions in human history, preventing more than 2 million deaths each year. Most licensed vaccines work by eliciting antibodies that can prevent infection by neutralizing the invading pathogen. However, vaccine-mediated induction of broadly neutralizing antibodies capable of thwarting infection with a highly mutable pathogen like HIV has proven exceptionally difficult in both humans and animal models. This shortcoming in vaccine success is likely due to intrinsic immune regulatory mechanisms that limit the quantity and quality of immune responses. Development of translational means to overcome these immunological roadblocks holds great promise for advancement of next-generation vaccines to prevent infection and improve global health. Our research focuses on the remarkable capacity of natural killer (NK) cells to suppress T and B cell responses. NK cells limit the magnitude and quality of adaptive immune memory triggered after immunization. This activity of NK cells impairs the generation of protective neutralizing antibody responses by restricting somatic mutation and affinity maturation of these antibodies within germinal centers. We find that a subset of transcriptionally unique NK cells migrates to sites of germinal center formation following immunization and contributes to suppression of follicular helper T cells (Tfh) differentiation via perforin-mediated elimination of activated CD4 T cells. We identify key effector molecules, receptors, and transcription factors that are putatively vital for this immunosuppressive activity of NK cells, and therefore represent innovative targets to enhance vaccine efficacy. The overall objective of this proposal is to test the scientific premise that cytotoxic functions of NK cells limit vaccine-mediated generation of HIV-specific broadly neutralizing antibodies. We propose three thematically connected aims that explore the contributions of various mediators that determine the cytotoxic immunoregulatory capacity of NK cells during immunization. In Aim 1, we will use cutting-edge knock-in mice to test the hypothesis that transient small molecule inhibition of NK-cell cytolytic function during immunization can safely and effective augment germinal center-mediated maturation of HIV-specific antibody responses. In Aim 2, we will use innovative bone marrow chimera and conditional knock-out mice to define the role of a network of transcription factors, chemokine receptors, and integrins in localization of NK cells near developing Tfh to facilitate cytolysis of these target cells. In Aim 3, we will use a new strain of mice and pioneering CRISPR-based screens to discover receptors involved in promotion or restraint of NK-cell killing of CD4 T cells. These experiments will define factors that enable and calibrate NK-cell suppression of adaptive immune responses during infection. Thus, the proposed work will facilitate subsequent development and deployment of innovative strategies to enhance HIV vaccine efficacy.